Magnetic translating device



June 2, 1970 I c, TiBB S 3,515,818

MAGNETIC TRANSLATING DEVICE Filed Jan. 25, 1962 2 Sheets-Sheet 1 I NVENTOR June 2, 1970 er 0. TIBBETTS MAGNETIC TRANSLATING DEVICE 2 Sheets-Sheet 2 Filed Jan. 23, 1962 United States Patent Oflice 3,515,818 Patented June 2, 1970 US. Cl. 179-114 25 Claims ABSTRACT OF THE DISCLOSURE A magnetic transducer having a unitary armature folded to provide two parallel arms. The end of one arm is attached to the case and this arm forms a part of the case. The end of the other arm is in a magnetic air gap and free to vibrate. The casing is flux conductive and in magnetic contact with permanent magnets which form the air gap. A drive pin is connected to the free end of the armature and extends through an aperture in the other arm of the armature. The armature is rigidly supported only at one end and a damper contacts the armature at the region of the fold.

This invention relates to magnetic translating devices having a movable armature and capable of translating mechanical to electrical energy or vice versa due to the operation of variable gaps and variable magnetic fluxes.

An object of this invention is to provide magnetic translating unit of very small compact size, while being highly stable and rugged.

Another object of the invention is to provide a magnetic transducer which in structure is self-encased in high permeability magnetic material so that the electrical coil and magnetic assembly are well shielded from external magnetic fields, and so that the transducer produces practically insignificant external magnetic fields.

A further object is to provide a magnetic translating device having its components welded together wherever possible, to provide mechanically stable joints of low magnetic reluctance.

Another object is to provide a magnetic translating unit having the supported part of its armature over the gaps at the free end of the armature, to have a stable unit relatively unaffected by aging or shock.

A further object of the invention is to provide a magnetic transducer useful as a microphone or receiver and having the desirable characteristics of very small size, high acoustic sensitivity, large bandwidth, and excellent flatness of response.

These objects are obtained by providing a magnetic translating device comprising an armature, means for supporting one part of the armature with another part free to vibrate, the armature being folded between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the free end of the armature, and means including structures of soft magnetic material providing a flux conductive path between said supporting means and said field establishing means.

More particularly, the magnetic translating device may be in the form of a transducer comprising a folded armature having one end fixed to an aperture plate, a plane of said end extending in the aperture, with the other end passing through an electrical signal coil and free to vibrate between magnets extending laterally of the plane of the free end on opposite sides thereof, the plate attached to a casing, the case, plate, and armature all being of soft magnetic materials, and substantially enclosing the magnets, coil, and armatures free end.

These and further objects of the invention will be apparent from the accompanying specification and drawings in which FIG. 1 is a section lengthwise of the translating device of this invention on line 1-1 of FIG. 3;

FIG. 2 is an exploded view of the invention;

FIG. 3 is a plan view;

FIG. 4 is an end view of the invention along line 4-4 of FIG. 3;

FIG. 5 is a plan view of a complete acoustic transducer including the translating device of this invention, along line '55 of FIG. 6;

FIG. 6 is a sectional view of the transducer of FIG. 5 along line 6-6 thereof;

FIG. 7 is a plan view on line 7-7 of FIG. 8 of a modified form of acoustic transducer utilizing the translating device of this invention; and

FIG. 8 is a sectional view of the transducer of FIG. 7 along line 8-8 thereof.

The particular embodiment of the translating device of this invention shown in FIGS. 14 comprises a lower case 1, a folded armature 2 having two arms with one end 3 fixed in recess 4 to plate 5 as by spot welding, the other armature end 6 free to vibrate between the upper and lower magnets 7 and 8 with pole pieces 9 having tapered pole faces 10, the pole pieces being spaced apart by shim spacers 11. When utilized as a transducer as in a preferred embodiment, the translating device may include a coil 12 through which the armature passes, such as the coil disclosed in Pat. No. 2,988,804 issued to Raymond W. Tibbetts. A drive pin 13 has a lower tongue extended through circular hole 14 of the free end of the armature and passes through armature hole 15 to a further driven or driving element such as the diaphragm of a microphone or receiver. Damping means 16 is seated in recess 17 of plate 5 and attached to the plate and armature as by adhesive. Vernier or fine magnetic adjustment disk 18 with slug 19 thereon is adjusted and then fixed in position to the case as by epoxy bonding. Insulated grommets 20 with apertures therethrough provide a passageway for the coil leads to the exterior of the case.

The case '1 and plate 5 as well as the disk 18 and slug 19 are made of soft magnetic materials, for example nickel-iron alloys. The upper portion or arm of the armature adjacent the fixed end substantially fills the complementary aperture 21 in plate 5 and thus completes the shielding of the coil. Any external stray flux collected by the upper surface of the armature is conducted almost entirely to the plate 5 and to the case 1, from which said flux extends outward to complete the path of the stray field. Because of the low reluctance of the armature and its junction with the plate, relative to the air gaps 22 and 23 and magnets 7 and 8, only a small residue of the stray flux is transmitted through the coil 12. Alternatively, the case, plate, and upper portion of the armature may be viewed as magnetic means providing an approximately 3 equipotential closed surface. In this manner the coil is substantially enclosed by soft magnetic material.

The pole pieces 9 comprise soft magnetic material of high permeability to carry both the static flux generated by the magnets 7 and 8 and the signal flux generated by or acting upon the coil. The magnets 7 and 8 extending laterally of the plane of the armatures free end on opposite sides thereof may comprise any suitable permanent magnetic material having sufficiently high coercive field and available magnetic energy. The magnets are magnetized approximately perpendicular to the plane of the free end of the armature, and have opposite poles facing each other across the gap in which the free armature end vibrates. The shims 11 spacing apart the pole pieces are made of essentially non-magnetic material, preferably a metal, such as an alloy containing chromium, appropriately attached to the pole pieces as by spot welding. The

drive pin 13 may be of any suitable material such as a metal or a plastic and is reduced in width where it enters the punched hole 14 to enable adhesive fillets to form on each side of the armature for a strong bond. The damping member 16 may be any material suitable for such purpose, but preferably is a highly plasticized vinyl; however any plasticized thermo plastic, silicone gel, elastomer or other flexible material having a lossy elastic modulus may be employed.

The tapered gaps 22 and 23 are defined by the pole pieces 9. The planes in which the faces lie, if extended back to the planes in which the adjacent opposing faces of the armature lie, intersect those latter planes in lines which substantially define a plane such that the virtual pivot axis of the armature lies substantially in the plane so defined. The latter plane is substantially perpendicular to the others, with very small gap angles. This provides optimum armature stability throughout large deflections of the armature, including contact with the pole pieces such that the armature would be in substantially flat contact at the extreme exent of its deflection. This enables the relative flux distribution in the gaps to remain essentially constant throughout the extent of the deflection of the armature. The pole pieces are tapered only at their central portion in the position of the projected area of the free end of the armature; the ends of each pole piece are flat and of constant thickness in order to be attached in abutting relation with the intermediate shim spacers. In other embodiments the tapered gaps could be formed by pole pieces of constant thickness, but tipped at an angle to the plane of the armature.

The operation of the translating device is as follows. When functioning as a driven unit, an endwise motion of the drive pin 13 caused by an external means will flex the free end of the armature between the magnets and pole pieces, causing opposite reluctance variations in the gaps 22 and 23 between the pole pieces and the armature, and consequent variations in the fluxes in the gaps, and hence in the armature. The pick-up or means to detect one or the other or both of such variations may be a unilateral element such as a magnetoresistive or Hall eflect device positioned in or at the vicinity of a gap, or may be bilateral in operation such as the coil 12 commonly employed in translating devices of this nature. When the coil is used, the changing flux in the armature will create an in the coil which can be led to further circuitry such as transistor amplifiers to utilize the signal as desired. When used as a driving element, the coil is employed; an alternating current through the coil will cause alternating flux in the armature, thereby flexing the armature toward one or the other of the pole pieces and thus reciprocating the drive pin 13 and any further elements to which the pin is attached; The armature moves throughout its extent beyond the fixed end to the free end.

The fixed end 3 of the armature is over the regions of the gaps. Hence any incidental rotation of the support of the fixed end results in a very small effective translation of the free end of the armature transversely in the gap between pole pieces 9. This is in contrast to straight armature designs in the prior art, in which the high sensitivity to rotation of the support of the armature is the chief cause of relatively poor stability upon aging and exposure to thermal shock and cycling. To be sure, the free end of the folded armature rotates as the support of the fixed end r tates, but the mechanical moment of magnetic origin augmenting this rotation is small, and furthermore, the change of gap reluctance with rotation is small, so that little static flux unbalance is caused in the armature by such rotation.

This advantage of the folded armature is of fundamental importance to stability, since it is much easier to support an armature without significant incidental translation than it is to fix or attach it in such a way as to avoid incidental rotation significant in the context of the prior art. It will be noted that the armature must be substantially free at the folded region in order for this advantage to obtain. Hence the damping means 16 must be flexible compared to the armature so that the formerwill not act significantly as a static constraint on the armature.

The function of the damping means 16 is to substantially eliminate the effect of the second natural mode of the armature, which tends to introduce a sharp dip in the frequency response of the device.

The stability of the device is further enhanced by welding as an attachment means wherever possible. In particular, the welding of the fixed end 3 of the armature to the recess 4 in the plate 5 is of first importance. Direct attachment at this region is made: possible by the magnetic configuration which enables the fixed end of the armature and the plate and case assembly to be placed at substantially the same magnetic potential. Preferably the joined elements are annealed for magnetic purposes subsequent to welding. The alloys utilized for the plate and armature are compatible, and the melting and diffusion which occur during welding result in a mechanically stable joint which after suitable annealing has low magnetic reluctance. Since the plate has to perform a different function from that of the armature in that it must carry a large amount of static flux, the use of separate pieces 'of appropriate dimensions and materials is generally desirable.

It will be noted that folding the armature back on itself makes possible the above objects and at the same time permits the device to have normal width, i.e. in the direction of line 4-4 in. FIG. 3. However, one end of the armature must of necessity lie outside the signal coil 12, which tends to increase the thickness of the device. This is overcome by providing the aperture 21 in the plate 5, in which lies the upper portion or arm of the armature except for its fixed end 3, with the armature extending little, if any, above the plate. As noted above, the coil 12 is not thereby appreciably exposed to external magnetic fields.

The assembly and testing of the translating device will be obvious to the artisan, and comprises appropriately attaching together the various components of the subassemblies such as the magnets, pole pieces and shims as well as the armature, coil, plate and so forth. Various testing procedures are performed at this stage of subassemlbly; then the subassemblies are gathered in the case Preferably spot welds are made through the sideof the case 1 to the edge of the plate 5 at various points about the periphery of the latter. Preferably also the bottom surface of the magnet 8 is bonded to the inside bottom of the case 1 by the thermal curing of a solids adhesive, such as an epoxy type, which had been preapplied as a fluid before the assembly of the subassemblies into the case. Further testing and adjustment of the vernier disk 18 with slug 19 thereon completes the preparation of the translating device as such.

The translating device finds particular application in very small microphones or receivers useful in hearing aids or other miniaturized circuitry. As shown in FIG. in a particular embodiment the translating device may be used to drive or be driven by a diaphragm for acoustic transduction. A frame 24 surrounds and is attached to the periphery of a layer 25 on sheet 26 as by epoxy adhesive. The layer 25 also defines diaphragm 27, at tached as by epoxy to the drive pin extending up therethrough, with the layer being removed from region 28 to define a flexible surround. An impedance tube 29 is carried by the frame and connects the two spaces on opposite sides of the diaphragm; the inside diameter of the tube is sufficiently large to enable substantial air flow back and forth during oscillation of the diaphragm. The function of such a Thuras tube is well known in the prior art. The frame is of a relatively rigid material such as brass, the sheet 26 may comprise a plastic such as a fluorocarbon resin, and the layer 25 may comprise a foil of aluminum adhered to the sheet by any appropriate means. Completing the transducer assembly is a cover 30 located by the frame and abutting the case. This may be fabricated of soft magnetic material similar to that used for the case and plate, to provide slight additional shielding of the coil from stray magnetic fields. Through the cover may be provided an acoustic aperture 31 serving as an additional acoustic impedance when the transducer is used as a microphone, or a similar aperture, or slot or notch, positioned on the side or elsewhere for leading to a tube such as the laterally extending tubes generally employed in receivers and some types of microphones.

The transducer of FIGS. 7 and 8 shows another embodiment providing improved transmission characteristics. The peripheral frame 32 omits a portion of the upper flat area carrying the impedance tube of the previous embodiment, and the layer '25- and the sheet 26 extend farther lengthwise of the transducer to define not only the diaphragm portion 27 but also the portion 33 carrying the flopper 34. The flopper 34 comprises the mass 35 supported by the flexible surround 36. Preferably a portion of the layer 25 underlies a portion of the mass 35, and the mass may have a vent 37 therethrough. Flopper surround 36, like diaphragm surround 38, comprises the sheet 26. In this modification the flopper supplants the impedance tube, and is a substantial improvement thereon. The mass 35 is acted upon by pressure difference between the two sides of the diaphragm, and is accelerated thereby, producing a volume displacement from one space to the other. Thus it acts primarily as an acoustic inertance, and is much superior to the impedance tube in that the resistive component of its impedance is negligible compared to that of a tube of equal inertance.

The energy loss due to the resistive component of the impedance tube has been a limiting factor in the performance of this type of transducer, as transducer size has been progressively reduced. It has proved practical to keep the stiffness of the surround 36 low enough, while maintaining mechanical positioning and stability of the mass 35, to provide a sufliciently low resonant frequency of the flopper, which must be less than the lower cutoff frequency of the transducer. The flopper may take a variety of configurations other than shown. The boss 3? provided on the mass element of the flopper is used to locate the mass; the boss is the preferred location of the vent, which extends between the spaces on opposite sides of the diaphragm.

Other embodiments employing the translating device of this invention may use solely a vent between the spaces separated by the diaphragm, or may use a combination of the flopper and the impedance tube in a single assembly.

Various modifications will be apparent to the artisan such as the relative dimensions, location, materials, configurations and the like. However, the invention is only to be limited by the scope of the appended claims.

I claim:

1. An electroacoustic transducer comprising an armature, means for supporting one part of the armature with another part free to vibrate, the armature being folded between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the free part of the armature, means including structures of soft magnetic material providing a flux conductive path between said supporting means and said field establishing means, a coil associated with said armature to enable transduction of mechanical to electrical energy and vice versa, a drive pin connected to said part of the armature free to vibrate and extending up through an aperture in the armature, a diaphragm connected to said drive pin, a frame supporting said diaphragm, and an impedance tube carried by said frame and connecting the spaces on the opposite sides of said diaphragm.

2. An electroacoustic transducer comprising an armature, means for supporting one part of the armature with another part free to vibrate, the armature being folded between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the free part of the armature, means including structures of soft magnetic material providing a flux conductive path between said supporting means and said field establishing means, a coil associated with said armature to enable transduction of mechanical to electrical energy and vice versa, a drive pin connected to said part of the armature free to vibrate and extending up through an aperture in the armature, a diaphragm connected to said drive pin, and an acoustic impedance adjacent the diaphragm in the form of a flopper comprising a mass supported by a flexible surround.

3. An electroacoustic transducer comprising an armature, means for supporting one part of the armature with another part free to vibrate, the armature being folded between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the free part of the armature, means including structures of soft magnetic material providing a flux conductive path between said supporting means and said field establishing means, a coil associated with said armature to enable transduction of mechanical to electrical energy and vice versa, a drive pin connected to said part of the armature free to vibrate and extending up through an aperture in the armature, a diaphragm connected to said drive pin, a frame supporting said diaphragm, and a cover of soft magnetic material located by the frame and adjacent at least one of said structures of soft magnetic material, said cover containing an acoustic aperture.

4. A magnetic translating device comprising: a pair of aligned spaced permanent magnets, a flux conductive shell interconnecting said pair, and an armature having a portion vibratable in a space between said magnets and extending from said space to said shell; said shell having a substantial aperture therein through which said portion and magnets would be exposed, said armature having another portion which substantially closes said aperture.

5. A magnetic translating device as in claim 4 further comprising a flux conductive member adjacent the shell, said member covering said aperture and said other portion.

6. An electromagnetic transducer comprising: a pair of aligned spaced permanent magnets; a flux conductive shell interconnecting said magnets through a pair of opposed faces adjacent respectively the outer poles of the magnet pair, one of said faces having an aperture therethrough; a coil within said shell; and a folded sheet armature having a portion vibratable in a space between said magnets and extending therefrom through the coil to the fold and thence to the shell, said armature having another portion which substantially closes said aperture.

7. A transducer as in claim 6 wherein said other portion is attached to the shell at an edge of said aperture adjacent one of said magnets.

8. A magnetic translating device comprising an armature, a case having an open side, a plate attached to the 7 case at the open side, the armature having one part attached to the plate with another part free to vibrate within the case, the plate having an aperture therethrough, a portion of the armature being positioned in and extending along the aperture to its attached part, the armature being folded between said parts, the region of the fold being free to vibrate, and means for establishing a magnetic field in the vicinity of the free part of the armature.

9. A transducer comprising an armature, a case having an open side, a plate attached to the case at the open side, the armature having one part attached to the plate with another part free to vibrate within the case, the plate having an aperture therethrough, a portion of the armature positioned in and extending along the aperture and being attached to the plate at said one part, the armature being folded between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the free part of the armature, and a coil associated with said armature to enable transduction of mechanical to electrical energy and vice versa.

10. An electromechanical transducer comprising an armature having a portion free to vibrate, means for establishing a magnetic field in the vicinity of said portion comprising a pair of magnets and a flux conductive shell interconnecting said pair, and a coil, said shell substantially enclosing said portion, said magnets and said coil, said shell also comprising another portion of the armature and having substantially the same magnetic potential throughout, the armature extending through said coil into contact with said shell.

11. A magnetic transducer comprising means including permanent magnets to establish a magnetic field in a gap, an armature having a first arm, the end portion of which extends into said gap, the armature having a second arm folded over said first arm, means for supporting said second arm at the end portion thereof in the proximity of said gap, the entire armature including said first arm and said second arm being otherwise unsupported and free to vibrate, and a coil surrounding said armature and secured relative to said field establishing means free of supportive contact with the armature.

12. A magnetic transducer as defined in claim 11, wherein the field establishing means include magnets with opposite poles opposed across the gap, and wherein structures of soft magnetic material provide a flux conductive path between the other poles of said magnets, the end portion of the second arm being attached to a portion of said structures.

13. A magnetic transducer as defined in claim 11, including damping means contacting the armature at a region between said arms, the damping means providing substantially no static constraint to the armature.

14. A magnetic transducer as defined in claim 11 wherein said field establishing means include pole surfaces defining tapered gaps between said surfaces and said end portion of the first arm.

15. A magnetic transducer comprising a case with a plate forming an attached cover therefor, means including permanent magnets to establish a magnetic field in a gap, said magnets being supported by the plate, an armature having a first arm, the end portion of which extends into said gap, the armature having a second arm folded over said first arm, said plate supporting said second arm at the end portion thereof in the proximity of said gap, the entire armature including said first arm and said second arm being otherwise unsupported and free to vibrate, and a coil surrounding said armature and secured relative to said field establishing means free of supportive contact with the armature.

16. A magnetic transducer as defined in claim 15 including damping means contacting the armature at a region between said arms, the damping means providing substantially no support to the armature.

17. A magnetic transducer as defined in claim 15, where- 8 in the magnets comprise a pair of magnets on opposite sides respectively of said gap.

18. A magnetic transducer as defined in claim 15, wherein the case, plate and armature are of soft magnetic material and have substantially the same magnetic potential throughout, and in combination substantially enclose the coil and magnets.

19. A magnetic translating device comprising an armature having a vibratable first portion, means for establishing a magnetic field in the vicinity of said first portion comprising a pair of magnets, a shell of soft magnetic material having a substantial part thereof interconnecting said magnets and conducting polarizing flux therebetween, another part of said shell comprising another portion of the armature, said another portion being located in an aperture defined by said first-named part of the shell and extending into contact with said first-named part of the shell, said shell substantially enclosing said first portion of the armature and said magnets.

20. A magnetic translating device as defined in claim 19, further comprising a coil through which the armature extends, said shell also substantially enclosing said coil.

21. A magnetic translating device as defined in claim 19, wherein said another portion of the armature extends into contact with the first-named part of the shell in the vicinity of said magnets.

22. A magnetic transducer comprising a pair of magnets having a gap therebetween, a shell of soft magnetic material having a substantial part thereof interconnecting said magnets and conducting polarizing flux therebetween, an armature having a vibratable first portion in said gap, another part of said shell comprising another portion of the armature located in an aperture defined by said firstnamed part of the shell, a coil, said armature being extended from the gap through said coil, being substantially reversed in direction, and being extended into contact with said first-named part of the shell, said shell substantially enclosing said coil.

23. A magnetic translating device comprising a case with a plate having an aperture therethrough and forming an attached cover therefor, means including permanent magnets to establish a magnetic field in a gap, an armature having a first arm, the end portion of which extends into said gap, the armature having a second arm folded over said first arm, positioned within the aperture and attached to the plate in the proximity of said gap, the entire armature including said first arm and said second arm being otherwise unsupported and free to vibrate, said case, plate and armature comprising soft magnetic material.

24. A magnetic transducer comprising a pair of permanent magnets, a shell of soft magnetic material having a substantial part thereof interconnecting said magnets, a coil within said shell, and an armature having a first portion vibratable in a space between said magnets and extending from said space through said coil, said part of the shell defining a substantial aperture through which said coil and said armature first portion would be exposed magnetically, another part of said shell comprising another portion of the armature which substantially closes said aperture and extends into contact with the first-named part of said shell, said first-named part of the shell comprising means for partially shielding magnetically the components within said shell, as well as means for conveying polarizing flux between the magnets and signal flux between said other portion of the armature and each magnet, said other portion of the armature comprising means for partially shielding magnetically said components as well as means for conveying signal flux.

25. An electromechanical transducer comprising an armature, means for supporting one part of the armature with another part free to vibrate, the armature being fold ed between said parts, the region of the fold being free to vibrate, means for establishing a magnetic field in the vicinity of the end portion of said free part of the armature, means including structures of soft magnetic mate- 9 10 rial providing a flux conductive path between said 811;!- 1,573,739 2/1926 ONeill 1791 19 porting means and said field establishing means, a coil 2,994,016 7/1961 Tibbetts et a1 1791l4 associated with said armature to enable transduction of 3,076,062 1/1963 F n 179-114 mechanical to electrical energy and vice versa, and a drive 3,111,563 11/1963 C l 1791 14 pin connected to said free part of the armature and extending with clearance through an aperture in the arma- 5 FOREIGN PATENTS 1,044,169 11/1958 Germany.

References c'ted 821,707 10/1959 Great Britain.

UNITED STATES PATENTS 786,754 4/1905 Graham 179--119 10 KATHLEEN H. CLAFFY, Primary Examiner 1,063,237 6/1913 Anderson 179119 

